fix: checking arduino ls response length when receiving userdata type

[Dosx001]

Keep getting this error non-stop when using arduino language server.

vim.schedule callback: .../dosx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/source.lua:358: attempt to get length of local 'response' (a userdata value)
stack traceback:
        .../dosx/.local/share/nvim/lazy/nvim-cmp/lua/cmp/source.lua:358: in function 'fn'
        [string "vim/_core/editor"]:273: in function <[string "vim/_core/editor"]:272>